Mainship 400 WOT

[Dougcole]

I've been reading/thinking about WOT recently. I very seldom run wide open, it's kind of worried me in the past. I do run at 80 to 85% throttle for about 40% of the time. As I've researched WOT though, I've come to believe that there are benefits to doing it occasionally.

My boat is a Mainship 400 with twin Yanmar 4LHA-STP, 240 hp each, 550 hours. I recently put in new exhaust elbows and mixers, flushed the RW cooling systems, had the intercoolers rebuilt, and had the valves adjusted. I've been wondering if all of this work has had a positive effect on the cooling system and performance in general. Today we were in calm water, no current, light load (1/2 fuel, 1/2 water), clean bottom. so I let her rip. Ran WOT for about 10 minutes, 3,500 RPM, trim tabs down all the way. 19.7 knots. 170 degrees on the temp gauges, nice and smooth.

I usually get about 15 knots at 2,900 rpm, so I was surprised at the jump from 600 RPM. I guess once you get "on a plane" the extra power makes a big difference.

I'm glad I did it, I have more confidence in my boat now.

 

[gaston]

I recently put in new exhaust elbows and mixers, flushed the RW cooling systems, had the intercoolers rebuilt, and had the valves adjusted


All that and under 550hours ??

 

[Dougcole]

I recently put in new exhaust elbows and mixers, flushed the RW cooling systems, had the intercoolers rebuilt, and had the valves adjusted


All that and under 550hours ??

Yeah. It was more of an age thing than an hours deal. My elbows were shot, the other stuff was preventative maintenance. The coolers were in good shape, they probably didn't need it, but a failure there is catastrophic, so I worried about it.

 

[sunchaser]

Gaston

Marine age counts too. On 14 year old systems just sitting wears a lot of stuff out. It certainly appears as if Doug is a very astute owner in tackling the tasks he just did.

 

[Baker]

Doug, just realize a LOT of power is realized in those engines way up at high RPMs. My point being....Max continuous power on those engines is 3100rpm. Power at 3100rpm is 190hp. Max rated power is 240hp at 3300rpm. So in that small little 200 rpm band lies 50 hp!!! And in your case that is multiplied by 2....not to mention the "overrun" up to 3500rpm(nothing wrong with that...it just means your are correctly propped with a little room to work with). So it is not surprising that you saw that much increase in speed at WOT. If you have access to the power curve charts of those engines, check it out.

 

[Keysdisease]

I know the guy who designed the 48 x 12 tabs on the back of your boat, nice to hear they do the job

Ran WOT for about 10 minutes, 3,500 RPM, trim tabs down all the way.

 

[Dougcole]

I know the guy who designed the 48 x 12 tabs on the back of your boat, nice to hear they do the job

I met that guy once at a boat show, is it you?

Baker, thanks for the info, very interesting. Sounds like I am OK running at 2900 RPM for long stretches? My calculations say it is about 85% of max power, and it is below the rated continious output.

 

[DavidM]

Running long term at 2,900 rpm if you are propped to reach a (phototached?) rpm of 3,500 rpm should be fine. If you do a little extrapolation of the prop curve up to 3,500 rpm then you are making about 120 hp each at 2,900 rpm.

But don't believe Yanmar's spec that you can run at 3,100 rpm continuously. That is marketing hype and is not realistic for decent life.

David

 

[Dougcole]

OK, thanks David, that's good info. My motors have always seemed happy at 2900, they don't shake, burn oil or run hot there, so I figured it was OK.

 

[Baker]

OK, thanks David, that's good info. My motors have always seemed happy at 2900, they don't shake, burn oil or run hot there, so I figured it was OK.

I ran my Pilot with one of those engines at 2900 all the time. I bought the boat with 150 hours and sold it with 1100. That thing ran perfectly. Most of the Yanmar gurus believe the 4LHA is one of the best engines Yanmar ever made.

 

[Dougcole]

Yeah, 5 years in and I love my little Yanmars. My favorite engines I've ever owned.

My Yanmar dealer says the same thing about them being one of the best motors Yanmar has ever made. He offered to buy them sight unseen if I wanted to do a repower. Said there is a huge market for them.